The present invention relates to improving efficiencies of an electric machine and, more particularly, to structure and methodology for optimizing the B+ connections of an alternator.
The rotor of an automotive alternator is typically driven by a belt and pulley system to rotate within stator windings coiled on a laminated iron frame. The magnetic field from the spinning rotor induces an alternating voltage into the stator windings. The alternating voltage (AC) is typically then converted to a direct current (DC) voltage by diode rectifiers that output the DC voltage to one or more batteries and to electrical devices of a vehicle. Such DC voltage being output by the alternator to the battery may be, for example, approximately 14 volts, which is generally at least one volt more than a conventional vehicle's battery voltage, for example 12.7 volts. The term “B+” refers specifically to the voltage at the battery positive post, as distinguished from the alternator output voltage. However, since the alternator output at the rectifier terminals is connected to the battery and the voltage drop in the charging/battery cable is generally low, the ‘connection’ between the alternator output and the battery positive terminal, as used herein, is referred to as the B+ connection because the charging/battery cable is connected to the battery B+ stud. For simplicity, any portion electrically common to the B+ connection may be referred to herein using the term B+ as a generic identifier.
Modern automotive alternators are generally required to supply ever-greater amounts of electrical current. For example, hybrid and electric vehicles may use electricity instead of internal combustion for driving the wheels, and an alternator may be combined with a starter in a mild hybrid configuration such as in a belt alternator starter (BAS) system. Other electrical loadings from air conditioning, electric power steering, and various vehicle systems further increase the required alternator electrical capacity. As a result, efficiency of automotive alternators needs to be optimized. Efficiency is generally limited by fan cooling loss, bearing loss, iron loss, copper loss, and the voltage drop in the rectifier bridges. The use of permanent magnets may increase efficiency by providing field flux without relying on a wound field that inherently creates ohmic losses. An alternator may have dual internal fans to improve operating efficiency and durability and to reduce heat-related failures. Many conventional alternator systems are addressed to such concerns. However, additional improvements may be obtained by reducing electrical resistances of B+ connections. By reducing electrical losses in the B+ connection(s), the electrical losses and thermal limitations of the rectifier circuit are also reduced.